In the prior art, molded or thermoformed face masks that cover the nose and mouth have been constructed of layers of fibrous sheet material and have found numerous applications in dirty or dusty environments, particularly in industry, but have also found use in areas of medicine such as with surgical masks. These masks are held on the face by one or more elastic bands or straps attached mechanically (such as by stapling), or by thermal fusing to the sides of the face mask to hold the mask to the face and to accomplish sealing of the mask over the nose and mouth. One desireable criterion of this type of mask is that it completely seals around the nose and mouth and allows no air to pass between the mask and the face. Too often, however, due to the softness and flexibility of fibrous sheet materials from which masks are molded, and due to the curved contour of the face between the bridge of the nose and the cheekbones, complete sealing around the bridge of the nose and mouth is not achieved except by making the masks more complex, which typically increases their cost. To solve this problem one technique is to affix foam rubber strips on the inner surface of the masks in the nose bridge area to achieve extra sealing. This is an extra manufacturing step that raises cost. Another technique to solving the sealing problem, though adding more complexity and manufacturing cost, is to affix a plastically deformable soft metal strip or clip on the outer surface of the mask on the nose bridge area, which strip or clip is squeezed over the bridge of the nose after the mask is put on to hold the mask to the face in the area around the nose. However, the use of the soft metal strip or clip is uncomfortable to some people because it doesn't easily adapt to changes in facial contours around the nose caused by facial movement due to speech or change of facial expression. Also, when there is a change in facial contour caused by speech or changed facial expression there is a tendency for air to leak between the face and the mask between the nose and cheekbones. This leakage fogs eyeglasses and safety glasses worn by the wearer of the mask, which is a detriment. To make the metal clip of a harder material which has more of a spring quality is not a solution since it introduces other problems. Furthermore, the use of a metal strip dictates that the user wear the mask over a high point on the nose in order to avoid excessive pressure over the nostrils which is undesireable. All these and other problems with prior art masks introduce another problem. It can be appreciated that if a mask is uncomfortable to wear, or creates a problem such as fogging, too often workers will not wear them even though use of a filter mask is dictated by the environmntal conditions in which the workers work.
In an attempt to eliminate the need for affixing foam rubber inserts on the inner surface of masks in the nose bridge area, and to attempt to eliminate the need for a metal clip or strip on the nose bridge portion of a mask, both done to achieve proper sealing, in the mask forming or molding process the prior art teaches more lightly compacting the fibrous sheet material from which the masks are fabricated in an area along the nose pad portions and the cheekbone areas of the mask as taught in U.S. Pat. No. 4,319,567 and shown in U.S. Pat. No. Des. 267,985. This, however, reduces the stiffness and shape retention capability of the mask in the area of the nose bridge portion. To compensate for this, the prior art also teaches (as shown in U.S. Pat. No. 4,384,577) forming or molding an elongated ridge member extending along and spaced from the edge or periphery of the mask and extending across the nose bridge portion of the mask between the nose pad portions on either side thereof to produce a spring action that enhances sealing between the mask and the wearer's face. However, all prior art mask shapes and varied compaction of the fibrous media from which the masks are formed for enhancement of the seal between the wearer's face and the mask utilize a planar mask periphery profile in the nose bridge--nose pad--upper cheekbone area. In contrast, the contour of the human face between the top of the nose and the upper part of the cheekbone is not a straight line. In fact, a straight line connecting any point in the upper cheekbone area and extending tangentially to the nose bridge shows a gap between the wearer's face contour and the straight line. The width of such a gap increases as the tangential line is moved downwards toward the tip of the nose.
The prior art also teaches the use of a molded, rubber like bead member extending around the periphery of a mask for providing a seal between the face of the wearer and the mask, as taught in U.S. Pat. No. 4,454,881.
Thus, there is a need in the art for a molded or thermoformed face mask that doesn't require extra manufacturing steps such as adding foam rubber or deformable soft metal strips in order to conform the mask to the contour of the human face and provide effective sealing, particularly in the area between the bridge of the nose and the cheekbones of the wearer of the mask. There is a need in the art for a mask that doesn't require extra manufacturing equipment, and the resulting extra manufacturing costs due to material and handling. There is also a need for a mask that eliminates the complexities and problems of prior art masks.